Nutrient contents assessment in a cloud forest terrestrial isopod (Ischioscia variegata), using a non-destructive method, X-ray fluorescence. Higher P and Ca in the isopods collected in the canopy

Abstract

We used X-ray fluorescence (XRF-EDS) associated to Scanning Electron Microscope (SEM) to evaluate the nutrient content of the terrestrial isopod Ischioscia variegata collected from three different areas of the Venezuelan cloud forest. Nutrients measures can provide information about the foraging dynamic of our target species between soil surface and canopy vegetation. Ischioscia variegata was chosen on the basis of its extensive geographical distribution in the Venezuelan mountains, high motility and vagility. This terrestrial isopod colonizes the litter layer of ground soil and most vegetation and epiphytes in the canopy of mountain cloud forests. In these habitats, it feeds on a decayed organic matter. Of the X elements analyzed, the percentage intensity ratios of calcium and phosphorus (I% Ca/I% P) proved capable of identifying the provenance of the specimen. The lower cuticle is the part of the body which shows the greatest sensitivity to variations in nutrient distribution from different habitats and phosphorus is the best marker revealing these environmental differences. Comparisons between the percentage intensity ratios of P and Si (I% P/I% Si) from the lower cuticle and the digestive contents are promising markers for separating isopod capture sites from habitat provenance. Isopods found in the canopy zone have higher concentrations of some nutrients compared with those collected from ground litter especially P and Ca.